Chromium electroplating bath including mist suppressors



United States Patent 3,423,297 CHROMIUM ELECTROPLATING BATH INCLUDING MIST SUPPRESSORS Johannes Martinus Arnold Van der Horst, ()lean, N.Y., assignor to Surface Research Incorporated, Olean, N.Y. No Drawing. Filed May 12, 1965, Ser. No. 455,310

US. Cl. 204-51 24 Claims Int. Cl. C231? 5 /06 ABSTRACT OF THE DISCLOSURE Halogenated organic ring compounds added in minor amount to chromium plating baths substantially eliminate atmospheric entrainment of chromic acid mist. The halogenated ring compounds do not alter the surface tension of the bath and prevent the formation of a foam on the surface of the bath incidental to the plating process.

This invention relates to means for suppressing atmospheric entrainment of liquid particles from aqueous solutions of inorganic salt in which bubbling is occurring. In particular, this invention is directed to the art of electrodepositing metallic chromium and pertains, more particularly, to additives for chromic acid baths which operate to suppress and substantially inhibit the formation of chromic acid mist or spray incidental to the electroplating process. However, it is to be understood that this invention is applicable to inorganic salt baths or solutions in general and may be used, for example, in anodizing baths or in any situation in which mist suppression is desired in connection with aqueous inorganic salt baths in which bubbling occurs.

The baths for the electrodeposition of metallic chr0- mium consists of rather concentrated aqueous solutions of chromic acid together with small percentages of sulfate, fluoride or fluosilicate anions. Because of the low efiiciency of chromium deposition, the high current densities required and the use of insoluble anodes, substantial liberation of hydrogen at the cathode and oxygen at the anode is experienced when electrolytically depositing chromium. These gases are evolved during electrolysis in the form of bubbles which burst violently at the surface of the concentrated chromic acid solution. The spray and mist resulting from this bubble bursting is of considerable volume and gives rise to serious problems, as is well known in the art.

In recent years, considerable success in suppressing mist has been obtained through the use of various surface active agents added to the chromic acid bath. The surface active agents reduce the surface tension of the bath so that the amount of spray entrained when the gas bubbles burst at the bath surface is reduced. At the same time, most of these surface active agents form a rather thick foam on the bath surface which further inhibits mist entrainment in the atmosphere. These surface active agents are, however, subject to certain disadvantages, principally loss due to volatility and/or breakdown in the presence of chromic acid, and the aggravation, in hard chrome plating, of pitting caused by base metal defects and the like. Moreover, the degree of mist suppression achieved by many of these agents, although substantial as compared with their non-use, is by no means of such order that atmospheric mist entrainment is eliminated or even substantially eliminated. It is, therefore, of primary concern in connection with this invention to provide an improved additive for chromic acid plating baths which is not subject to the above disadvantages and which, at the same time, suppresses mist formation to a greater degree than heretofore accomplished. Essentially, the present in- Patented Jan. 21, 1969 vention consists of an additive in the form of a halogenated ring compound which is soluble in the aqueous chromic acid chromium plating solution.

The ring compounds may be monocyclic or polycyclic compounds in which halogen atoms are bound to nuclear carbon atoms. Although the mechanism by which the mist suppressing effects of the present invention are achieved is not known, it appears that alteration of surface tension plays little or no part in the effect. Further, no foam or protective blanket is formed by the additives of this invention.

The monocyclic halogenated compounds of this invention may be saturated or unsaturated alicyclic compounds (cycloalkanes, cycloalkenes, and cycloalkadienes); they may be aromatic; or they may be heterocyclic. The polycyclic compounds may be bicyclic or they may consist of an heterocyclic ring fused to an aromatic ring. In each, the halogen is bound to nuclear carbon atoms. In addition, the compounds must be water soluble to the extent that individually, or cumulatively, they represent in solution at least about .006 gram per liter of the aqueous plating solution.

The chromic acid solutions with which the present invention is usable may vary widely in composition, the following aqueous solutions being representative:

Bath A Grams per liter of aqueous solution Chromic acid (CrO 250 H 2.5 Trivalent chromium (Cr 6.0

Bath B Chromic acid (CrO Bath C Econochrome H SO 1.5

Bath D Unichrome HCR 710 335 EXAMPLE I To Bath A was added 0.1 gram of 1,4,5,6,7,7 hexachlorobicyclo-(2,2,1)hept-5-ene-2,3-dicarboxylic acid per liter of bath. Electrolysis was conducted in the resulting solution at a plating current of 7.5 a-mperes per liter of solution; and at a solution temperature of 60 C. Mist formation was reduced by 95100% as compared with solutions not containing the hexachlor0bicyclo(2,2,1) hept-S-ene-2,3-dicarboxylic acid.

EXAMPLE II The conditions of Example I were repeated using .125 gram of octachlorocyclopentene per liter of plating solution in place of the 1,4,5,6,7,7 hexachlorobicyclo(2,2,l) hept-5-ene-2,3-dicarboxylic acid of Example I. The results were substantially identical in the two examples.

EXAMPLE III Example I was repeated using .1 gram of bis(pentaehlorocyclopentadienyl) per liter of solution, with substantially identical results.

EXAMPLE IV Example I was followed using .1 gram of hexachlorocyclopentadiene dissolved in 1.25 milliliter propanol per liter of solution, with substantially identical results.

EXAMPLE V Example -I was followed using .15 gram of l-oxy- 2,3,4,5-hexachloro-Z-cyclopentene dissolved in 1.25 milliliter methylethylketone, with substantially identical results.

EXAMPLE VI Example I was followed using .1 gram of para dichlorobenzene dissolved in 1.25 milliliter propanol per liter of solution, with substantially identical results.

EXAMPLE VII Example I was followed using .15 gram of 5,7-diiod- 8-hydroxyquinoline per liter of solution, with substantially identical results.

EXAMPLE VIII Example I was followed using .1 gram of Z-methoxy- 4,6-bis(isopropylamino)-s-triazine per liter of solution, with substantially identical results.

EXAMPLE IX Example I was followed using .1 gram of hexachlorocyclohexane dissolved in 1.25 milliliter propanol per liter of solution, with substantially identical results.

EXAMPLE X Example I was followed using .1 gram of pentachlorophenol dissolved in 1.25 milliliter trichloroethane per liter of solution, with substantially identical results.

EXAMPLE XI Example I was followed using .1 gram of l-methoxypropanol-2,3,6-trichlorobenzene per liter of solution, with substantially identical results.

EXAMPLE XII Example I was followed using .1 gram of tetrachlorothiophene dissolved in 1.25 milliliter propanol per liter of solution, with substantially identical results.

EXAMPLE XIII Example I was followed using .1 gram of 3,4,5-trichloro-2-furoyl chloride dissolved in 1.25 milliliter propanol per liter of solution, with substantially identical results.

EXAMPLE XIV To Bath A was added .05 g. of octachlorocyclopentene, .025 g. of l,4,5,6,7,7 hexachlorobicyclo(2,2,1)hept-S-ene- 2,3-dicarboxylic acid, and .025 g. of perchlorocyclopentadecane per liter of bath. Electrolysis was conducted in the resulting solution at plating currents of 2.5, 5, 7.5 and 10 amperes per liter of solution and at a solution temperature of 60 C. In all cases, mist formation was reduced 95-100% as compared with solution not containing the aforementioned addition.

EXAMPLE XV T0 Bath A was added .125 g. of octachlorocyclopentene per liter of bath. Electrolysis was conducted in the resulting solution at a plating current of 7.5 amperes per liter of solution and at solution temperatures of 45 C., 50 C., 55 C., 60 C. and 70 C. In all cases, mist formation was reduced by 95100% as compared with solutions not containing octachlorocyclopentene.

EXAMPLE XVI To each of Baths A, B, C and D was added .05 gram of octachlorocyclopentene, .025 gram of 1,4,5,6,7,7-hexachlorobicyclo(2,2,1)hept-5-ene-2,3-dicarboxylic acid, and .025 gram of perchlorocyclopentadecane per liter of bath. Electrolysis was conducted in the resulting solution at a plating current of 7.5 amperes per liter of solution and at a solution temperature of 60 C. In all cases mist formation was reduced by 95-100% as compared with solutions not containing additions.

EXAMPLE XVII Example I was followed using .1 milliliter of orthodichlorobenzene per liter of solution. Mist formation at the anode was reduced by -95%, but mist formation at the cathode was hardly reduced, as compared with solutions not containing orthodichlorobenzene.

EXAMPLE XVIII Example I was followed using .1 milliliter of 1,2,4,5, 6,7,8-octachloro-3u,4,7,7a tetrahydro-4,7-methanoindene per liter of solution. Mist formation at the cathode was reduced by 90-95%, but mist formation at the anode was hardly reduced.

EXAMPLE XIX Example I was followed using .05 milliliter of orthodichlorobenzene (Example XVII) and .05 milliliter of octachloro-tetrahydro'methanoindene (Example XVIII) per liter of solution. Overall mist formation was reduced by -100%.

EXAMPLE XX Example I was followed using .1 g. heptachlorotetrahydro-4,7-methanoindene per liter of solution. Mist formation was reduced by 20-25%.

EXAMPLE XXI Example I was followed using .1 g. heptachlorotetrahydro-4,7-methanoindene dissolved in 1.25 ml. propanol per liter of solution. Mist formation was reduced by 95- EXAMPLE XXII Example I was followed using .15 g. 1,3 dibromo-5,5- dimethylhydantoin per liter of solution. Mist formation was reduced by 20-25%.

EXAMPLE XXIII Example I was followed using .15 g. of 1,3-dibromo- 5,5 dimethylhydantoin dissolved in 1.25 ml. acetone per liter of solution. Mist formation was reduced by 70-75%.

EXAMPLE XXIV Example I was followed using .15 ml. of dichlorohexafluorocyclobutane per liter of solution. Mist formation was reduced by 10-15%.

EXAMPLE XXV To Bath A was added .15 ml. of dichlorohexafluorocyclobutane per liter of bath. Electrolysis was conducted in the resulting solution at a plating current of 7.5 amperes per liter of solution and at a solution temperature of 20 C. Mist formation was reduced by 90-95%.

EXAMPLE XXVI Example I was followed using .1 g. polyvinylpyrrolidone per liter of solution. Mist formation was reduced by 95-100%.

EXAMPLE XXVII Example I was followed using .1 g. bis(2,6-phenol)- 4,4-isopropylidene per liter of solution. Mist formation was reduced by 90-95%. The same experiment in the same solution was repeated after a 5 day interval. Mist suppression was reduced only by 50-55%.

EXAMPLE XXVIII EXAMPLE XXIX Example I was followed using .1 gram of 1,3-dioxy- 4,5,6,7 tetrachloroisobenzofuran dissolved in 1.25 milliliter ammonia per liter of solution, with substantially identical results.

EXAMPLE XXX Example I was followed using .1 gram of tetrachloro- 1,2-pyrone per liter of solution, with substantially identical results.

EXAMPLE XXXI To Bath A was added 0.1 gram of 3,4-dichlorotetrahydrothiophene-l,l-dioxide per liter of bath. Electrolysis was conducted in the resulting solution at a plating current of 7.5 amperes per liter of solution and at a solution temperature of 45 C. Mist formation was reduced by 9095% as compared with solutions not containing 3,4- dichlorotetrahydrothiophene 1,1-dioxide.

EXAMPLE XXXII Example I was followed using .01 gram pentachloro phenol, .01 gram 6,7,8,9,l0,l0 hexachloro l,5,5,6,9,9 hexahydro 6,9 methano 2,4,3 benzodioxathiepin-3- oxide, .01 gram cyanuric chloride, .01 gram hexachlorocyclopentadiene, .01 gram 2,3,6 trichlorobenzyloxypropanol, .01 gram 0,0 dimethyl-O-2,4,S-trichlorophenylphosphorothioate, .01 gram heptachlorotetrahydro-4,7- methanoindene, .01 gram di(pchlorphenyl) methylcarbinol, .01 gram 2-methoxy-4,6 bis (isopropylamino)-striazine, .01 gram dimethylamino salt of 2,3,6-trichlorobenzoic acid dissolved in 1 milliliter methylethylketone per liter of solution, with substantially identical results.

As will be evident to those skilled in the art, a number of the halogenated compounds enumerated above have limited solubility in aqueous media. I have found that compounds according to this invention are active as mist suppressors only to the extent that they are soluble in aqueous media and that the compounds preferably represent, in solution, at least about .025 gram per liter of solution in order to achieve substantially complete mist suppressing effect. However, as is illustrated in Example XXVIII, mist suppression is evident down to as little as about .006 gram of additive per liter of bath, and this trend is general throughout the examples. Further I have found that the mist suppressing effect of compounds according to this invention is substantially additive when the compounds are used simultaneously. Thus, in cases where a compound or compounds according to this invention are soluble in aqueous media to an extent less than about .025 gram per liter of solution, several compounds may be combined. An example of this effect is set forth in Example XXXII. In this manner, halogenated compounds according to this invention which have a very limited solubility in aqueous media may still be usefully employed if they are accompanied by one or more other halogenated compounds according to this invention in amounts sufficient to complement their lack of solubility and to bring the total amount of soluble compounds up to at least about .025 gram per liter of solution.

Further I have found that the mist suppressing effect of some compounds according to this invention is relatively greater at the anode of an electrolytic cell, while the mist suppressing effect of some other compounds according to this invention is relatively greater at the cathode of an electrolytic cell. An example of greater mist suppression at the anode is set forth in Example XVII. An example of greater mist suppression at the cathode is set forth in Example XVIII. I have found however that when a compound according to this invention suppressing mist at the anode, and a compound according to this invention suppressing mist at the cathode are added simultaneously to a solution-operating as an electrolytic cell for which mist suppression is desired, the resulting mist 6 suppression is complete. An example of this is set forth in Example XIX.

Further, I have found that of many compounds according to this invention which have a very low solubility in water, the mist suppressing effect can be enhanced considerably by first dissolving the said compound in a suitable solvent other than water and then adding the resulting solution to the aqueous medium for which mist suppression is desired. As will be clear to those skilled in the art, the nature and quantity of the solvent should be carefully chosen so as not to interfere with the main process. For instance, propanol when added to a chrome plating solution will reduce hexavalent chromium to trivalent chromium. Thus, when excessive amounts of propanol are used as a solvent for the mist suppressor, the trivalent chromium content of the solution will rise beyond acceptable limits. An example of this effect using propanol as a solvent is set forth in Examples XX and XXI. An example of this effect using acetone as a solvent is set forth in Examples XXII and XXIII.

I have further found that the mist suppressing effect is preferably but not necessarily limited to ring compounds having at least five atoms in the nucleus. However, ring compounds with less than five nuclear atoms are more volatile and therefore easily escape from the solution, thus limiting their usefulness. An example is set forth in Example XXIV. When however, the process is carried out at a lower temperature, these more volatile compounds clearly exhibit their mist suppressing effect. An example is set forth in Example XXV.

I have found that the mist suppressing effect is produced by the presence of the ring compound and not by its halogenation. An example of this effect is set forth in Example XXVI. However, non-halogenated ring compounds can only be used for mist suppression in solutions which do not chemically attack the ring. Chromium plating solutions for instance, oxidize most non-halogenated rings. An example of this effect is set forth in Example XXVII. The presence of halogen atoms bound to nuclear carbon protects the ring from chemical attack, and increasingly so as more such halogen atoms are present.

I have further investigated the minimum amount of said ring compounds necessary to produce a noticeable mist suppressing effect, and have found that whereas at a concentration of .00625 of ring compound per liter of solution the effect is still noticeable, at a concentration half as great or .003215 gram per liter of solution the mist suppressing effect can hardly be detected. An example of this effect is set forth in Example XXVIII.

I have also found that the mist suppressing effect according to this invention is not limited to use in connection with chromic acid solutions, but may be usefully employed to suppress atmospheric entrainment of mist in connection with other inorganic salt solutions as well. To illustrate, two identical solutions of 25% (by volume) nitric acid (69.4% HNO were prepared, to one of which was added .1 gram per liter of the mixture of compounds set forth in Example XVI. To each solution was added two grams of low carbon steel. The solution to which the halogenated ring compounds was added developed substantially less spray (liquid particles carried into the atmosphere) although it is to be noted that the evolution of gaseous fractions was the same in both cases. To illustrate a commercial use, the following example is given.

EXAMPLE XXXIII A conventional anodizing solution was prepared, consisting of 25% (by volume) of sulfuric acid (technical grade) in water. This solution was electrolyzed at 15 amperes per liter and 11 volts for 15 minutes, during which time a heavy mist or spray was developed. Then, .1 gram per liter of mixture consisting of 16 parts of chlorendic acid, 4 parts of octachlorohexachlorohexane was added to the solution. Electrolyzing under the above conditions was resumed with only a trace of spray or mist being developed.

This invention is characterized b the fact that the formation of surface foam for mist suppression purposes is entirely eliminated. Loss of additives according to this invention occurs only as incidental to loss of the solution itself. As a result, periodic replenishing of the additive is required only after long intervals.

It is to be understood that certain changes and modifications as illustrated and described may be made without departing from the spirit of the invention or the scope of the following claims.

What is claimed is:

1. In an aqueous inorganic chromic acid chromium electroplating bath in which gas bubbles are generated the improvement comprising an additive in said bath molecularly dispersed therein in a small amount sufiicient to substantially eliminate atmospheric entrainment of liquid particles due to bubble bursting at the surface of the bath, said additive having at least limited solubility in the bath, which sustantially retains the surface tension of the bath and which is incapable of producing a foam on the surface of the bath, said additive being selected from the group consisting of 1,4,5,6,7,7-hexachlorobicyclo-(2,2,1)-hept-5-ene-2,3-

dicarboxylic acid; octachlorocylclopentene; bis (pentachlorocyclopentadienyl) 1,-oxy-2,3,4,5-hexachloro-Z-cyclopentene; paradichlorobenzene; 5,7-diiodo-8-hydroxyquinoline; 2-meth0xy-4,6-bis(isopropylamino)-s-triazine; hexachlorocyclohexane; pentachlorophenol; 1-methoxypropanol-2,3,6-trichlorobenzene; tetrachlorothiophene; 3,4,5-trichloro-2-furoyl chloride; perchlorocyclopentadecane; orthodichlorobenzene; 1,2,4,5,6,7,8-octach1oro-3,4,7,7-tetrahydro-4,7-methanoindene; octachlorotetrahydromethanoindene; heptachlorotetrahydro-4,7-methanoindene; 1,3-dibromo-5,S-dimethylhydantoin; dichlorohexafiuorocyclobutane; polyvinylpyrrolidone; bis(2,6-phenol)-4,4-isopropylidene; 1,3-dioxy-4,5,6.7-tetrachloroisobensofuran; tetrachloro-1,2-pyrone; 3,4-dichlorotetrahydrothiophene-1,l-dioxide; 6,7,8,9,10,10-hexachloro-1,5,5,6,9,9-hexahydro-6,9-

methano-2,4,3-benzdioxatl1iepin-3-oxide; cyanuric chloride; hexachlorocyclopentadiene; 2,3,6-trichlorobenzyloxypropanol; 0,0-dimethyl-O-2,4,5-trichlorophenylphosphorothioate; di (p-chlorophenyl methylcarbinol; dimethylamino salt of 2,3,6-trichlorobenzoic acid; and mixtures thereof.

2. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of 1,4,5,6,7,7-hexachlorobicyclo- (2,2,1)-hept-5-ene-2,3-dicarboxylic acid sufiicient to inhibit atmospheric entrainment of chromic acid mist.

3. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of octachlorocyclopenten sufficient to inhibit atmospheric entrainment of chromic acid mist.

4. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of bis(pentachlorocyclopentadienyl) suflicient to inhibit atmospheric entrainment of chromic acid mist.

5. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of hexachlorocyclopentadiene sufiicient to inhibit atmospheric entrainment of chromic acid mist.

6. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of 1-oxy-2,3,4,5-hexachloro-2- cyclopentene suflicient to inhibit atmospheric entrainment of chromic acid mist.

7. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of para dichlorobenzene sufficient to inhibit atmospheric entrainment of chromic acid mist.

8. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of 5,7-diiodo-8-hydroxyquinoline sufiicient to inhibit atmospheric entrainment of chromic acid mist.

9. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of 2-methoxy-4,6-bis(isopropylamino)-s-triazine sufficient to inhibit atmospheric entrainment of chromic acid mist.

10. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of hexachlorocyclohexane sufficient to inhibit atmospheric entrainment of chromic acid mist.

11. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of pentachlorophenol sufiicient to inhibit atmospheric entrainment of chromic acid mist.

12. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of l-meth0xypropanol-2,3,6-trichlorobenzene sufiicient to inhibit atmospheric entrainment of chromic acid mist.

13. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of tetrachlorothiophene sutficient to inhibit atmospheric entrainment of chromic acid mist.

14. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of 3,4,5-trichloro-2-furoyl chloride suificient to inhibit atmospheric entrainment of chromic acid mist.

15. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of a mixture of octachlorocyclopentene, 1,4,5,6,7,7-hexachlorobicyclo(2,2,1)hept-S-ene- 2,3-dicarboxylic acid, and perchlorocyclopentadecane sufficient to inhibit atmospheric entrainment of chromic acid mist.

16. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of orthodichlorobenzene sufficient to inhibit atmospheric entrainment of chromic acid mist.

17. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solu tion and a small amount of 1,2,4,5,6,7,8-ocetachloro-3ot, 4,7,7a-tetrahydro-4,7-methanoindene sufiicient to inhibit atmospheric entrainment of chromic acid mist.

A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solutron and a small amount of a mixture of orthodichlorobenzene and 1,2,4,5,6,7,8-octachloro-3a,4,7,7a-tetrahydro- 4,7-methanoindene sufiicient to inhibit atmospheric entrainment of chromic acid mist.

19. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of heptachlorotetrahydro-4,7- methanoindene sufficient to inhibit atmospheric entrainment of chromic acid mist.

20 A bath for the electrodepositon of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of 1,3-dibromo-5,5-dimethylhydantoin suflicient to inhibit atmospheric entrainment of chromic acid mist.

21. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of dichlorohexafluorocyclobutane sufficient to inhibit atmospheric entrainment of chromic acid mist.

22. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of 1,3-dioxy-4,5,6,7-tetrachloroisobensofuran sufficient to inhibit atmospheric entrainment of chromic acid mist.

23. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of tetrach1oro-1,2-pyrone sufficient to inhibit atmospheric entrainment of chromic acid mist.

24. A bath for the electrodeposition of chromium comprising an aqueous chromic acid chromium plating solution and a small amount of 3,4-dichlorotetrahydrothiophene-1,1-dioxide suflicient to inhibit atmospheric entrainment of chromic acid mist.

References Cited UNITED STATES PATENTS 2,714,124 7/1955 Maude et a1 260648 2,750,334 6/ 1956 Brown 204-51 2,750,337 6/1956 Brown et a1. 20451 2,846,380 8/1958 Brown 20451 2,900,420 8/ 1959 Lidov 260648 3,312,613 4/ 1967 Mark 260648 2,842,488 7/ 1958 Strauss et a1 2045 1 XR 15 JOHN H. MACK, Primary Examiner.

G. KAPLAN, Assistant Examiner.

US. Cl. X.R. 

